Question: What controls patterns in MAOM content in forest soil?

Expectations:

1. Climate and soil characteristics will explain most of the patterns in MAOM content and stability, and these controls vary by site and over large spatial scales.

- Warmer sites and sites with more clay and iron oxides will have greater concentrations of MAOM.

- MAOM turnover will be more strongly controlled by mineralogy, with more clay-rich and iron-rich sites having the oldest and most stable MAOM.

Counterpoint: Warmer sites should also have smaller standing nutrient pools, which may lead to more root exudation from trees, or mining by associated fungi, as a way to liberate nutrients from MAOM. This may result in smaller, more dynamic MAOM stocks with relatively short turnover times.

2. Within-site patterns in tree mycorrhizal association will explain a smaller but still important amount of variation in MAOM content and turnover time.

- ECM-dominated plots will have less MAOM than AM-dominated plots

- ECM-dominated plots will have shorter MAOM turnover times than AM-dominated plots (because ECM taxa may be able to liberate mineral-bound SOM)

Introduction

Study design: Soils collected in seven forested NEON sites across the Eastern U.S. (Fig 1). At each site, soils were collected within 6-7 plots that spanned a range of AM vs ECM tree dominance:

Site Characteristics

Site MAT (C) MAP(mm) Dominant tree species Soil % clay (Mean +/- SD) Soil Fe (ox-extractable)
LENO 18.1 1386 American Sweetgum, American Hornbeam, Possumhaw 44.7 +- 13.8 1.0 +- 0.4
DELA 17.6 1372 Water oak, Red maple, Sugarberry 37.0 +- 6.3 0.88 +- 0.2
ORNL 14.4 1340 Red maple, Sour gum, Chestnut oak 22.0 +- 12.7 0.13 +- 0.05
SERC 13.6 1075 Tulip poplar, American Beech, American Sweetgum 17.4 +- 6.2 0.27 +- 0.1
HARV 7.4 1199 Eastern Hemlock, Northern Red Oak, American Beech 5.5 +- 1.9 0.38 +- 0.1
BART 6.2 1325 American Beech, Eastern Hemlock, Red maple 3.6 +- 0.7 0.76 +- 0.5
TREE 4.8 797 Sugar maple, Red maple, Gray alder 5.4 +- 1.1 0.34 +- 0.09
  proportion.C_HF mg.C.per.g.soil_HF
Predictors Estimates std. Error std. Beta standardized std. Error p std. p Estimates std. Error std. Beta standardized std. Error p std. p
(Intercept) 0.881 0.061 0.023 0.137 <0.001 0.864 32.631 8.890 0.009 0.238 <0.001 0.971
E -0.254 0.093 -0.410 0.126 0.006 0.001 -7.715 9.516 -0.019 0.108 0.418 0.861
CDI -1.833 1.621 0.069 0.157 0.258 0.659 -653.508 242.244 -0.638 0.251 0.007 0.011
FeOx 0.071 0.029 0.383 0.154 0.013 0.013 12.467 3.524 0.556 0.157 <0.001 <0.001
E * CDI 4.585 2.572 0.212 0.119 0.075 0.075 208.762 266.007 0.080 0.102 0.433 0.433
Random Effects
σ2 0.004 37.966
τ00 0.000 Site 28.290 Site
ICC 0.045 0.427
N 7 Site 7 Site
Observations 46 46
Marginal R2 / Conditional R2 0.362 / 0.391 0.348 / 0.627
  proportion.N_HF mg.N.per.g.soil_HF
Predictors Estimates std. Error std. Beta standardized std. Error p std. p Estimates std. Error std. Beta standardized std. Error p std. p
(Intercept) 0.884 0.044 0.028 0.115 <0.001 0.805 1.652 0.432 0.025 0.181 <0.001 0.892
E -0.196 0.070 -0.239 0.119 0.005 0.045 -1.140 0.544 -0.022 0.106 0.036 0.834
CDI 0.601 1.183 0.493 0.134 0.612 <0.001 -28.027 11.681 -0.237 0.196 0.016 0.227
FeOx 0.014 0.021 0.092 0.138 0.503 0.503 1.000 0.193 0.771 0.149 <0.001 <0.001
E * CDI 4.381 1.946 0.252 0.112 0.024 0.024 32.087 15.169 0.213 0.101 0.034 0.034
Random Effects
σ2 0.002 0.127
τ00 0.000 Site 0.046 Site
ICC   0.269
N 7 Site 7 Site
Observations 46 46
Marginal R2 / Conditional R2 0.430 / NA 0.502 / 0.635

  proportion.C_OLF mg.C.per.g.soil_OLF
Predictors Estimates std. Error std. Beta standardized std. Error p std. p Estimates std. Error std. Beta standardized std. Error p std. p
(Intercept) 0.012 0.042 -0.024 0.171 0.766 0.887 1.786 1.709 -0.016 0.170 0.296 0.926
E 0.148 0.062 0.339 0.144 0.018 0.018 4.496 2.451 0.247 0.131 0.067 0.059
CDI 1.768 1.125 0.066 0.193 0.116 0.732 -37.926 45.900 -0.454 0.190 0.409 0.017
FeOx -0.009 0.020 -0.081 0.182 0.656 0.656 1.485 0.810 0.313 0.171 0.067 0.067
E * CDI -2.933 1.731 -0.230 0.135 0.090 0.090 -87.733 68.221 -0.159 0.124 0.198 0.198
Random Effects
σ2 0.002 2.663
τ00 0.000 Site 0.371 Site
ICC 0.082 0.122
N 7 Site 7 Site
Observations 46 46
Marginal R2 / Conditional R2 0.158 / 0.227 0.267 / 0.357
  proportion.N_OLF mg.N.per.g.soil_OLF
Predictors Estimates std. Error std. Beta standardized std. Error p std. p Estimates std. Error std. Beta standardized std. Error p std. p
(Intercept) 0.029 0.026 -0.032 0.132 0.263 0.808 0.091 0.055 -0.008 0.185 0.101 0.964
E 0.107 0.041 0.203 0.137 0.010 0.140 0.080 0.078 0.136 0.135 0.302 0.314
CDI 0.155 0.699 -0.388 0.154 0.824 0.012 -1.835 1.489 -0.475 0.205 0.218 0.021
FeOx 0.006 0.012 0.075 0.158 0.635 0.635 0.048 0.026 0.326 0.179 0.069 0.069
E * CDI -2.550 1.150 -0.286 0.129 0.027 0.027 -1.604 2.163 -0.095 0.128 0.458 0.458
Random Effects
σ2 0.001 0.003
τ00 0.000 Site 0.000 Site
ICC   0.149
N 7 Site 7 Site
Observations 46 46
Marginal R2 / Conditional R2 0.255 / NA 0.213 / 0.330
  proportion.C_FLF mg.C.per.g.soil_FLF
Predictors Estimates std. Error std. Beta standardized std. Error p std. p Estimates std. Error std. Beta standardized std. Error p std. p
(Intercept) 0.108 0.045 -0.012 0.130 0.017 0.926 3.827 1.849 -0.014 0.209 0.039 0.945
E 0.106 0.071 0.264 0.130 0.136 0.042 2.613 2.318 0.180 0.122 0.260 0.141
CDI 0.039 1.208 -0.157 0.150 0.974 0.296 -66.957 50.028 -0.486 0.226 0.181 0.032
FeOx -0.061 0.021 -0.437 0.152 0.004 0.004 0.030 0.824 0.006 0.171 0.971 0.971
E * CDI -1.726 1.965 -0.107 0.122 0.380 0.380 -44.265 64.686 -0.079 0.116 0.494 0.494
Random Effects
σ2 0.002 2.299
τ00 0.000 Site 0.863 Site
ICC 0.014 0.273
N 7 Site 7 Site
Observations 46 46
Marginal R2 / Conditional R2 0.335 / 0.344 0.269 / 0.469
  proportion.N_FLF mg.N.per.g.soil_FLF
Predictors Estimates std. Error std. Beta standardized std. Error p std. p Estimates std. Error std. Beta standardized std. Error p std. p
(Intercept) 0.086 0.034 -0.017 0.124 0.011 0.893 0.148 0.064 -0.013 0.208 0.022 0.951
E 0.088 0.054 0.191 0.129 0.100 0.139 0.066 0.083 0.112 0.128 0.430 0.383
CDI -0.756 0.905 -0.416 0.145 0.404 0.004 -2.470 1.739 -0.491 0.226 0.155 0.030
FeOx -0.020 0.016 -0.185 0.149 0.214 0.214 0.008 0.029 0.046 0.177 0.794 0.794
E * CDI -1.831 1.489 -0.149 0.121 0.219 0.219 -1.233 2.317 -0.064 0.121 0.595 0.595
Random Effects
σ2 0.001 0.003
τ00 0.000 Site 0.001 Site
ICC   0.242
N 7 Site 7 Site
Observations 46 46
Marginal R2 / Conditional R2 0.339 / NA 0.231 / 0.417 
ggarrange(propC.myc.flf, propC.myc.olf, propC.myc, nrow=1, ncol=3, common.legend=T, legend="right", labels=c("a", "b","c"))
## `geom_smooth()` using formula 'y ~ x'
## `geom_smooth()` using formula 'y ~ x'
## `geom_smooth()` using formula 'y ~ x'
## `geom_smooth()` using formula 'y ~ x'

ggsave("som.proportion.plots.tiff",path="figures/", width= 30, height= 10, units="cm")
concC.fe.hf=ggplot(final_data, aes(x=FeOx, y=mg.C.per.g.soil_HF, color=Site))+
   geom_smooth(method="lm",size=2, se=F)+
  geom_point()+
  labs(x=" % FeOx ", y="[MAOM C] (mg/g soil)", colour="Site")+
  theme_cowplot()+
  theme(legend.title=element_text(hjust=0.5, size=16), legend.text=element_text(size=15), axis.text=element_text(size=15), axis.title=element_text(size=19))

concN.fe.hf=ggplot(final_data, aes(x=FeOx, y=mg.N.per.g.soil_HF, color=Site))+
   geom_smooth(method="lm",size=2, se=F)+
  geom_point()+
  labs(x=" % FeOx ", y="[MAOM N] (mg/g soil)", colour="Site")+
  theme_cowplot()+
  theme(legend.title=element_text(hjust=0.5, size=16), legend.text=element_text(size=15), axis.text=element_text(size=15), axis.title=element_text(size=19))

ggarrange(concC.fe.hf, concN.fe.hf, nrow=2, ncol=1, common.legend=T, legend="right", labels=c("a", "b"))
## `geom_smooth()` using formula 'y ~ x'
## `geom_smooth()` using formula 'y ~ x'
## `geom_smooth()` using formula 'y ~ x'

ggsave("hf.conc.fe.tiff",path="figures/", width= 14, height= 20, units="cm")
  C.N_FLF C.N_OLF C.N_HF
Predictors Estimates std. Error std. Beta standardized std. Error p std. p Estimates std. Error std. Beta standardized std. Error p std. p Estimates std. Error std. Beta standardized std. Error p std. p
(Intercept) 22.908 5.411 -0.001 0.172 <0.001 0.998 20.352 7.346 -0.005 0.201 0.006 0.982 20.317 2.785 -0.017 0.149 <0.001 0.908
E 9.057 7.804 0.420 0.134 0.246 0.002 15.486 9.709 0.506 0.130 0.111 <0.001 7.802 3.389 0.170 0.082 0.021 0.040
CDI 81.259 145.316 0.111 0.192 0.576 0.562 186.418 198.175 0.187 0.219 0.347 0.393 -229.967 75.440 -0.783 0.160 0.002 <0.001
FeOx -6.095 2.569 -0.412 0.174 0.018 0.018 -3.414 3.374 -0.179 0.177 0.312 0.312 0.659 1.216 0.063 0.117 0.588 0.588
E * CDI -35.993 217.148 -0.021 0.126 0.868 0.868 -98.413 270.697 -0.045 0.123 0.716 0.716 -162.162 94.601 -0.134 0.078 0.086 0.086
Random Effects
σ2 27.040 40.775 4.890
τ00 3.555 Site 11.218 Site 2.132 Site
ICC 0.116 0.216 0.304
N 7 Site 7 Site 7 Site
Observations 46 46 46
Marginal R2 / Conditional R2 0.243 / 0.331 0.230 / 0.396 0.633 / 0.745
  mg.C.per.g.soil_HF mg.N.per.g.soil_HF
Predictors Estimates std. Error std. Beta standardized std. Error p Estimates std. Error std. Beta standardized std. Error p
(Intercept) 15.302 3.428 0.011 0.281 <0.001 1.228 0.185 0.002 0.204 <0.001
plotBA 0.562 1.179 0.062 0.130 0.634 -0.027 0.079 -0.052 0.151 0.733
Random Effects
σ2 52.173 0.257
τ00 39.699 Site 0.045 Site
ICC 0.432 0.148
N 7 Site 7 Site
Observations 46 46
Marginal R2 / Conditional R2 0.004 / 0.434 0.003 / 0.150

Correlations.

Fraction modern has no relationship with soil, plant, or climate variables but is inherently different on a site-by-site basis. It also has no bearing on the concentration or proportion of MAOM C in the soil. This is interesting because we hypothesized there would be a connection between the concentration of C in the MAOM fraction and the age of that C (bigger pool, more buidling up= older C and smaller pool= more dynamic pool= younger C) but that does not seem to be the case! :

  fractionModern
Predictors Estimates std. Error std. Beta standardized std. Error p std. p
(Intercept) 1.05 0.06 -0.02 0.38 <0.001 0.953
FeOx 0.01 0.01 0.15 0.15 0.314 0.314
E -0.04 0.04 -0.06 0.12 0.409 0.634
CDI -1.77 1.71 -0.38 0.39 0.300 0.335
E * CDI 0.86 1.23 0.08 0.12 0.483 0.483
Random Effects
σ2 0.00
τ00 Site 0.00
τ11 Site.E 0.00
ρ01 Site -1.00
N Site 6
Observations 39
Marginal R2 / Conditional R2 0.235 / NA
  fractionModern fractionModern
Predictors Estimates std. Error std. Beta standardized std. Error p Estimates std. Error std. Beta standardized std. Error p
(Intercept) 0.99 0.02 -0.03 0.38 <0.001 0.98 0.05 -0.02 0.36 <0.001
mg.C.per.g.soil_HF 0.00 0.00 0.19 0.12 0.125
proportion.C_HF 0.03 0.06 0.05 0.11 0.642
Random Effects
σ2 0.00 0.00
τ00 0.00 Site 0.00 Site
ICC 0.71 0.67
N 6 Site 6 Site
Observations 39 39
Marginal R2 / Conditional R2 0.030 / 0.717 0.002 / 0.671 

## `summarise()` has grouped output by 'plotID', 'mycType'. You can override using the `.groups` argument.`geom_smooth()` using formula 'y ~ x'

## `geom_smooth()` using formula 'y ~ x'
  CNratio
Predictors Estimates std. Error std. Beta standardized std. Error p
(Intercept) 69.630 9.646 -0.379 0.351 <0.001
E -9.701 6.604 -0.092 0.063 0.142
Random Effects
σ2 204.895
τ00 Site 462.144
ICC 0.693
N Site 6
Observations 96
Marginal R2 / Conditional R2 0.008 / 0.695